The present invention pertains generally to syringes for medical use. More particularly, the present invention pertains to syringes having a self-sheathing needle. The present invention is particularly, but not exclusively, useful for syringes having a safety sheath that can be releasably locked over the tip of the syringe needle.
The American Dental Association (ADA) attributes most needlestick and subsequent infections in dental offices to the handling of sharp instruments and needles which must be handled carefully to prevent injuries and recapped after use. If a patient requires multiple injections from a single syringe, the needle should be recapped between each use to preclude the possibility of needlestick injury. At best, needles may be recapped by placing the cap in a special holder, by using forceps or other appropriate instrument to grasp the cap, or by simply laying the cap on the instrument tray and then manually guiding the needle into the cap until it is completely sealed. The greatest risk of needlestick injury occurs when the cap must be manually placed over the used needle. Almost 90% of needlestick injuries occur either when the operator withdraws the needle from the patient, or between injections. Operators usually do not bother to take the time to re-cap the needle between injections, and leave the bare infected needle uncovered on the tray, and this is precisely when accidents occur.
The lack of passive devices specifically designed for injury prevention has shown itself to be one of the greatest obstacles in preventing operator exposure to infected blood and bodily fluids. According to a clinical report published in the September 1997 issue of JADA, during a 63-month period, in which 423 parenteral exposures to blood and bodily fluids were documented, dental students and dental assistants had the highest rate of exposure; syringe needle injuries were the most common type of exposure; and giving injections, cleaning instruments after procedures and drilling were the activities most frequently associated with exposure. According to a study published in the July 1998 report of the CDC, 17% of all needlestick injuries to New York City healthcare workers occurred among dental workers, and 10%-18% of these latter injuries resulted in HB infection.
In light of the above, it is an object of the present invention to provide devices suitable for the purposes of injecting a medicament in a safe, efficient manner. It is another object of the present invention to provide a syringe having a disposable needle cartridge that remains in a locked guarded configuration until engagement with a syringe body. It is yet another object of the present invention to provide a syringe that passively resheaths and locks after use. It is yet another object of the present invention to provide a self-sheathing needle cartridge that can be used in conjunction with a re-useable syringe body and a standard medicament cartridge. Yet another object of the present invention is to provide a self-sheathing dental needle which is easy to use, relatively simple to manufacture, and comparatively cost effective.
The present invention is directed to a self-sheathing dental needle and a method for using a self-sheathing dental needle. For the present invention, the dental needle includes a cylindrically shaped syringe body that surrounds a chamber and defines a cylinder axis. The chamber is open at both its distal and proximal ends and the syringe body is formed with an exterior surface. A first finger grip is permanently affixed to the exterior surface of the syringe body near the proximal end. Further, the chamber is sized to hold a medication cartridge with an adequate amount of fluid medicament. A plunger is provided for insertion into the proximal end of the syringe body and for engagement with the medication cartridge to apply a force upon the fluid medicament in the medication cartridge.
In addition to the first finger grip, a second finger grip is slideably mounted on the exterior surface of the syringe body. Specifically, the second finger grip is oriented to allow the second finger grip to move relative to the syringe body in a direction that is parallel to the cylinder axis. Preferably, the second finger grip includes a curved proximal portion for engagement with a finger, a distal tang, and a substantially straight section connecting the curved portion to the tang. When the second finger grip is fully advanced in the distal direction, the tang is positioned near the distal end of the syringe body. Additionally, a portion of the tang extends outwardly in a radial direction from the cylinder axis. A spring that is mounted on the syringe body biases the second finger grip in the distal direction.
The self-sheathing dental needle of the present invention also includes a needle cartridge that is engageable with the syringe body. Specifically, the needle cartridge includes two parallel offset needle sections with an interconnecting midsection that provides for fluid communication between the sections. A first needle section is formed with an end extending in the distal direction from the midsection, and the second needle section is formed with an end extending in the proximal direction.
The midsection of the needle is encased in a needle holder to rigidly attach the needle to the needle holder. The needle holder includes a cylindrically shaped section positioned over the second section of the needle and centered on the second axis. For the present invention, the cylindrical section of the needle holder extends beyond the second section of the needle in the proximal direction to guard the end of the second section of the needle. Additionally, the diameter of the cylindrical section is sized to fit over the distal end of the syringe body and create a tight seal between the syringe body and the cylindrical section when the needle cartridge is engaged with the syringe body. The needle cartridge further includes a sheath that is disposed over the first section of the needle and slideably mounted on the needle holder. Preferably, the sheath is substantially shaped as an elongated cylinder having a lumen. Specifically, the sheath is centered on the first axis and slideably mounted on the holder to allow the sheath to move relative to the holder and in the direction of the first axis. For this purpose, the sheath is disposed within a hole provided in the holder. A guide can be mounted on the needle and disposed within the lumen of the sheath to maintain the sheath centered on the first axis. The midsection of the needle passes through a slit in the sheath. Preferably, the slit extends axially along the sheath to allow the sheath to move relative to the needle.
The needle cartridge further includes a spring enclosure that is mounted to the needle holder. Preferably, the spring enclosure is substantially cylindrically shaped and mounted on the needle holder proximal to the second section of the needle and centered on the first axis. The distal end of the spring enclosure is open, while the proximal end is closed. As such, a coil spring can be disposed within the spring enclosure for compression between the sheath and the proximal end of the spring enclosure. With this cooperation of structure, the coil spring in the spring enclosure biases the sheath in the distal direction. Preferably, the inner diameter of the spring enclosure is of sufficient size to allow the sheath to travel within the spring enclosure.
An important aspect of the present invention is a lock that forms a part of the cartridge. For the present invention, the lock is formed with a lock body having a distal end for attachment to the proximal end of the sheath, and a proximal end that engages the distal end of the coil spring in the spring enclosure. The lock body is sized relative to the inner diameter of the spring enclosure to allow the lock body to travel within the spring enclosure.
A locking tab extends radially from the lock body to create a hinged connection between the locking tab and lock body. As such, the locking tab is moveable between a locking configuration in which the tab is in an unstressed state and extends away from the first axis, and a release configuration in which the tab is biased to a position where the tab is relatively closer to the first axis. Thus, upon the application of an appropriate force, the tab can be moved from the locking configuration to the release configuration, and upon release of the applied force the tab will attempt to return to the locking configuration.
When the locking tab is in the locking configuration, translation of the lock body and sheath relative to the needle is blocked. Specifically, the locking tab abuts against the distal edge of the spring enclosure to thereby limit proximal motion by the sheath and lock body relative to the needle. Additionally, the lock body is preferably sized to be larger than the hole formed in the needle holder. As such, the lock body abuts against the needle holder to prohibit distal motion by the sheath and lock body relative to the needle, when the locking tab is positioned distal to the spring enclosure.
The locking tab is formed with a cam surface for the purpose of reconfiguring the locking tab from the locking configuration to the release configuration. The cam surface is formed on the distal side of the locking tab and oriented at an angle to the first axis. As such, a force directed parallel to the first axis can be applied to the cam surface to reconfigure the locking tab from the locking configuration and into the release configuration.
To assemble and use the self-sheathing dental needle, first the fluid medicament and plunger are inserted into the chamber of the syringe body. Next, the second finger grip is advanced in the distal direction relative to the syringe body until the tang is positioned near the distal end of the syringe body. At this point, the syringe body is prepared for engagement with a needle cartridge. For this purpose, a needle cartridge as described above that includes a needle, needle holder, sheath, guide, spring enclosure, spring, lock body and locking tab is prepared with the locking tab in the lock configuration. As such, the sheath is positioned to extend distally over the end of the first section of the needle to guard against accidental needle sticks.
Once the syringe body and needle cartridge have been prepared for engagement, the distal end of the syringe body can be inserted into the cylindrical portion of the needle holder to create a tight seal between the holder and syringe body. As such, the end of the second section of the needle will be positioned in fluid communication with the chamber of the syringe body. If a medicament cartridge is used, the second section of the needle and the medicament cartridge can be adequately sized to ensure that the end of the second section of the needle penetrates the medicament cartridge when the syringe body is inserted into the needle holder.
To unlock the sheath, the cartridge is first rotated about the cylinder axis relative to the syringe body to align the tang of the second finger grip with the locking tab. Specifically, the cartridge is rotated to position the tang adjacent to the cam surface of the locking tab. This rotation will result in the tang being positioned distal to the locking tab. Next, the second finger grip can be slid in the proximal direction relative to the syringe body. Upon initial movement of the second finger grip, the tang is caused to contact the cam surface of the locking tab and bias the locking tab into the release configuration. In the release configuration, the locking tab is no longer blocked by the spring enclosure, and accordingly, the sheath and lock body are able to translate in the proximal direction relative to the needle.
Continued movement of the second finger grip in the proximal direction causes the tang to engage the locking tab and pull the lock body and sheath in the proximal direction. The spring enclosure is formed with an axial slit to allow the tang to remain in contact with the locking tab as the second finger grip pulls the lock body and a portion of the sheath into the spring enclosure. This proximal movement by the second finger grip, sheath and lock body will be resisted by the spring on the syringe body and the spring in the spring enclosure. Eventually, movement of the second finger grip in the proximal direction will be stopped by the syringe body, leaving the second finger grip positioned directly opposite the syringe body from the first finger grip. When the second finger grip is moved to this position, the sheath retracts over the first section of the needle to expose the end of the first section of the needle. Only the spring in the spring enclosure prevents further retraction of the sheath.
With the end of the first section of the needle exposed, the user can insert the end of the needle into a patient for an injection. Needle penetration depth is not limited to the exposed portion of the needle because the sheath is able to retract as the user applies force to the syringe to press the needle into the patient. At this point, only the spring in the spring enclosure resists the retraction of the sheath. To inject the patient with the fluid medicament, the plunger is depressed into the chamber of the syringe body to expel medication from the chamber, through the needle and into the patient. For this purpose, the finger grips can be used to offset the force required to depress the plunger into the chamber.
When the needle is removed from the patient, the spring in the spring enclosure expands to force the sheath to return to the position where only a portion of the needle is exposed. At this point, the user can give the patient another injection or release the second finger grip to fully cover the first section of the needle by the sheath. Specifically, upon release of the second finger grip, the spring mounted on the syringe body will further expand to translate the second finger grip, lock body and sheath distally until the lock body abuts against the needle holder. This distal movement of the lock body will cause the locking tab to move to a position distal to the edge of the spring enclosure, reconfiguring the locking tab back into the locking configuration from the release configuration and repositioning the sheath over the end of the first section of the needle. At this point, relative movement between the sheath and the needle is blocked by the locking tab (i.e. the sheath will be locked in position over the end of the first section of the needle). Once the sheath is safely locked over the end of the first section of the needle, the syringe can be stored safely for later use or the needle cartridge can be removed from the syringe body and discarded. Upon removal of the needle cartridge, the syringe body can be autoclaved for reuse.